NONADIABATIC EFFECTS IN THE PHOTODISSOCIATION AND ELECTRONIC SPECTROSCOPY OF HMN(CO)(3)(DAB) - QUANTUM WAVE-PACKET DYNAMICS BASED ON AB-INITIO POTENTIALS

The photochemistry of many transition metal complexes is governed by a multitude of electronically excited states, coupled by various mechan isms. For the transition metal complex HMn(CO)(3)(dab) (dab = 1,4-diaz a-1,3-butadiene) the photoreactivity (cleavage of the Mn-H bond) and e lectronic absorption spectra are characterized on the basis of quantum mechanical first-principles calculations. In a first step, the A ' gr ound (singlet) and the three lowest electronically excited (triplet) p otential curves along the Mn-H bond distance are computed using the CA SSCF/CCI method. Two of the excited states are found to be bound and a re of the metal-to-ligand charge transfer type, whereas the third, lig and-to-ligand charge transfer state is repulsive. In the relevant ener gy region, two avoided crossings are observed, indicative for strong n onadiabatic couplings. In a second step, the UV/vis photochemistry of the complex is investigated by means of nuclear wave packet dynamics, We solve the nonadiabatically coupled, time-dependent Schrodinger equa tion in a diabatic representation for different initial conditions to determine both photodissociation yields and electronic absorption spec tra. In particular, the effect of the nonadiabatic couplings on the el ectronic absorption spectrum and on the photoreactivity is investigate d.